The invention relates generally to sterilization devices, and more particularly it relates to a sterilization apparatus for infusion solutions and the like, stored in containers arranged on open shelves of a displaceable rack; the apparatus is of the type that employs a closed housing adapted for receiving the rack with the containers and within the housing, a fan for whirling around a heated gaseous working medium or fluid, and a cooling device for subsequent indirect cooling of the whirling operating fluid. Sterilization devices of this kind are described for example, in the journal "Die Pharmazeutische Industrie" 1975 Volume 10/pages 825-829, Volume 11/pages 909-912, Volume 12/pages 1071-1075.
In this apparatus, saturated steam, if necessary mixed with air, is introduced as the operating medium or fluid, or whirled air is heated directly in the apparatus. In employing steam it is necessary to avoid a sudden pressure drop during cooling, due to the condensation of steam that might entail a risk of explosion of the hot container exposed to a high inside pressure, by admixing air or other gaseous media.
An increased need for sterile infusion solutions and the like requires as economic an operation of sterilization devices as possible under strict requirements, and furthermore, in order to prevent damage of mostly extremely sensitive substances to be sterilized, the prescribed operational conditions during the entire operating time must be exactly fulfilled. The strictness of maintaining the prescribed operating conditions in sterilizing has been still further increased in view of the development of new and still more sensitive sterilization solutions and the like, and also to diminish erroneous handling in sterilizing conventional substances. It is especially important that the time period during which the sterilized substance is subjected to high temperatures be reduced to such a short sterilizing time as is absolutely necessary in order to avoid any damage; that means that the heating and the cooling of the apparatus must be as rapid as possible, or in other words, a reduction of the heating and cooling periods is necessary.
It has been found that by making use of a hitherto conventional and substantially uniform whirling movement of the operating fluid around the substance to be sterilized, certain values of the heating-up and cooling-down times may not be exceeded. Since the hot operating medium streaming through the rack supporting the containers of the sterilization devices, for example from below the rack to above the rack, transfers more heat at its point of entry than at its point of exit, the containers located on the lower-most shelf of the rack are heated to the sterilization temperatures more quickly, than the containers located on the uppermost shelf. The sterilization time to be maintained can naturally be counted from that point only at which all containers have reached the sterilization temperature. As in the subsequent cooling step the cooled operating medium absorbs more heat from the hot containers in the vicinity of its inlet point than near its outlet point, nonetheless, the heating and the cooling times of the containers follow different characteristic curves, and consequently containers arranged on different shelves of the rack are unavoidably subjected to the sterilizing temperature for different time periods.